Slice the onion as thinly as possible. Mix it with the ingredients of the dressing in a bowl and set aside.
Cook the pasta following its instructions and drain it when done.
While the pasta is cooking, trim the asparagus to remove any dry ends but don't remove too much. You should just slice the ends off thinly - if necessary. Cut the Asparagus into pieces and place them into a pan. Add 2 tsp olive oil, minced garlic and a pinch of pepper. Saute the asparagus for a few minutes over medium heat. You want to cook it gently, so it still has a bite to it.
Your pasta and asparagus should be done at about the same time. Add the pasta, asparagus and onions with the dressing into a large bowl and give it a gentle mix.
Serve immediately or let it cool down fully and serve chilled. Scatter 1tbsp of freshly chopped parsley over it just before serving.
This salad can be served as main, and in that case, this recipe is enough for 2 portions.